Insect herbivory differentially affects the behaviour of two pollinators of Brassica rapa.

Pollinator behaviour during floral visits shapes plant mating opportunities, influencing the likelihood of outcrossing versus selfing. These behaviours may be affected by plant responses to antagonists such as insect herbivores. This study aimed to better understand how insect herbivory affects visitation behaviour of two pollinator community members of field mustard (Brassica rapa): the buff-tailed bumblebee (Bombus terrestris) and the large cabbage white butterfly (Pieris brassicae). In field tent experiments, we allowed caterpillars of P. brassicae to develop from leaf-feeding early instars to flower-feeding late instars and assessed pollinator response to undamaged and damaged plants during 10-min observations. We recorded behaviours with potential effect on outcrossing: (first) choice and overall plant preference, plant visit duration, number and duration of flower visits per plant, and distance travelled between plant visits. Bumblebees visited more plants and flowers, but spent less time per flower than butterflies did. Bumblebees often travelled to neighboring plants, whereas butterflies often flew longer distances to reach a next plant. Herbivory by large florivorous caterpillars altered butterfly plant choice-mostly towards plants with caterpillars, but not their behaviour on the plant. Bumblebees did not alter their choices, but changed their behaviour on the plant: they visited more flowers on plants with herbivory. However, herbivory by small leaf-feeding caterpillars did not affect the behaviour of either pollinator. Our results show that pollinator community members respond differently to herbivory and that this response changes over time, potentially affecting plant mating patterns.